Conventional pneumatic tires for wheeled vehicles, such as automobiles and trucks, rely on a single air chamber inflated at uniform pressure for both operational economies and absorption of road shocks and bumps. However, shock absorption is accomplished most effectively with relatively low pressure tires, whereas improved fuel economy, driving range, acceleration, cruising speed, ease of steering and durability of the tires are more aptly achieved with relatively high pressure tires. Therefore, conventional single chamber tires are a compromise between inherently conflicting requirements.
The present invention relates to pneumatic tires for wheeled vehicles, and more particularly to an improved tubeless pneumatic tire provided with a pair of concentric annular air chambers inflated at different air pressures, the pressure in the outermost chamber being higher than the pressure in the innermost chamber. The present invention thus provides a design which separates the two conflicting requirements of a pneumatic tire so that each of these two requirements can be met separately and in a more optimum fashion; a relatively low-pressure inner chamber is provided for efficient shock-absorption, and a relatively high-pressure outer chamber is provided for operating efficiency and economy. At the same time, the essential balloon-like flexion of a single-chamber tire is retained through a dual-chamber structure which includes no internal dividers or other components which restrict, impede or obstruct the flexion and shock-absorption of any portion of the sidewalls or tread area of the tire.
Attempts have been made in the past to design pneumatic tires with multiple air chambers, as disclosed, for example, in U.S. Pat. Nos. 2,196,814, 2,525,752, 2,735,471 and 2,925,845, in British Patent Specification No. 347,690, in German Patent Publication Nos. 2,517,895 and 2,430,638, and Japanese Patent No. 34-5751. Such designs provide multi-chamber pneumatic tires which are structurally divided by heavy, rigid or semi-rigid partitions in fixed locations and shapes, and which, therefore, require complex and costly molds and processes for manufacturing, resulting in heavy inert structures using a large volume of solid rubber or other casing material as compared to the volume of air contained in the air chambers, with the resulting inconvenience of high cost raw materials, a critical lack of flexibility in the resulting tires, heavy inertial masses in rotation, and substantial constant friction and deformation of elastomeric material causing considerable heating. These prior designs also fasten together or otherwise anchor various areas of the sidewalls or tread through rigid, semi-rigid or structurally inert dividers or reinforcements, so that the essential balloon-like bowing and flexion of a single-chamber tire is lost. In the FIG. 1 embodiment of German Patent Publication No. 2,430,638, the sidewalls are tied together with a partition wall which is stretched under tension into a straight line, so that the sidewalls cannot freely bow away from one another.
Other designs have been proposed for pneumatic tires such as disclosed in U.S. Pat. Nos. 2,780,266, 2,508,596, 2,560,609 and 2,480,463, and in the aforementioned German Patent Publications, for example, which are, for all practical purposes, directed to concentrically mounting a pair of pneumatic tires, one within the other, with the added complication of rendering such compound pneumatic tires incapable of being mounted on conventional wheel rims.
Further efforts in designing multi-chamber pneumatic tires are represented by structures such as disclosed in U.S. Pat. No. 1,989,402 wherein a pneumatic tire having much analogy with a conventional tire is provided with an auxiliary tread mounted thereon by rivets, or other fasteners, such auxiliary tread being provided with a built-in air chamber, and in U.S. Pat. No. 2,850,069 there is a teaching of a multi-chamber inner tube for pneumatic tires requiring special rims or special retaining flaps mounted within the inner tube.
However, all prior art has failed to integrate the major features necessary to effectively combine fuel efficiency and effective shock-absorption, including (1) unimpeded and unobstructed flexion of the tread and sidewalls of the tire comparable to that of a conventional single-chamber tire, (2) minimum bulk and weight, (3) an elastically-deformable and collapsible diaphragm with no internal or external supports of a fixed, rigid or semi-rigid nature, (4) optimum relative size of the chambers, (5) a relatively large cross-section and floor for the low-pressure chamber, (6) convenient, secure and independent control of pressures in individual chambers, (7) simplicity of design, and (8) safety features to minimize and contain blowouts of high-pressure tires.